#318 Remove popovers from CKAN 2.0

After some chat we've decided that the popover code was a little too noisy and was waaay too over the top for the issue that it was trying to solve.

Here's the problem it was trying to solve: context within activity streams and the ability to unfollow/follow items quickly. 

Here's the reasoning for removing it:

1. It appears in a way that is un-expected to the user. It's a hover item that appears whilst hovering on a link. It's not really ideal. People expect a tooltip... but not a whole popover which obscures content that they might be trying to read.
2. It creates a load of visual noise for something that should be simple
3. It's easy to show one... but fiddly to hide (requires hitting a close icon)
4. They don't work on non-hover devices (e.g. phones, tablets, etc.)

Ultimately if we still think that people should be able to unfollow/follow things quickly we should investigate a better solution for this problem or perhaps roll this into `ckanext-pdeu` as upposed to core.